Hydraulic system having area controlled bypass

ABSTRACT

The present disclosure is directed to a hydraulic system having a first source of pressurized fluid and at least one fluid actuator. The hydraulic system further includes a first valve disposed between the first source and the at least one fluid actuator. The first valve is configured to selectively communicate pressurized fluid from the first source to a tank in response to a first command. The first command is at least partially based on a predetermined flow area of the first valve.

TECHNICAL FIELD

The present disclosure is directed to a hydraulic system and, moreparticularly, to a hydraulic system having area controlled bypass.

BACKGROUND

Work machines such as, for example, excavators, dozers, loaders, motorgraders, and other types of heavy machinery typically use one or morehydraulic actuators to accomplish a variety of tasks. The actuators arefluidly connected to one or more pumps that provide pressurized fluid tochambers within the actuators. An electro-hydraulic valve arrangement istypically connected between the pumps and the actuators to control aflow rate and direction of pressurized fluid to and from the chambers ofthe actuators.

The electro-hydraulic valve arrangements often include eithersingle-valve or multi-valve arrangements. Single valve arrangementstypically include a valve having only two positions with fixed flowareas to direct flow into and out of the chambers. Single-valvearrangements may also include a bypass orifice which directs fluid flowfrom the pump to a reservoir which may provide a desired feedback to anoperator. Operator feedback may occur during a resistive movement of theactuator, such as when the load on the actuator increases, e.g., when awork implement transitions from soft soil to hard soil. A resistivemovement of the actuator increases the pressure within the hydraulicsystem which causes an increase in fluid flow through the bypass orificeto the reservoir. As such, an operator may sense a slower movement ofthe actuator and/or a machine component, may sense the need to furtheractuate a control lever to move an associated component, may sense anengine surge to increase the supply of fluid to the hydraulic system,and/or may sense a variety of other operational changes.

Multi-valve arrangements provide increased flexibility over single-valvearrangements by allowing independent control of fluid into and out ofeach chamber of an actuator. Multi-valve arrangements may not, however,include bypass orifices and thus may adversely affect feedback to anoperator during work machine operation.

Additionally, the pumps that may supply fluid to the actuators oftenrequire a continuous flow of fluid therethrough to maintain lubricationand cooling of the pump. Furthermore, in multi-pump systems, someactuators may only require pressured fluid from one pump, while otheractuators may require pressurized fluid from more than one pump.Accordingly, unnecessary fluid flow may be supplied within portions of ahydraulic system, resulting in unwanted pressure increases, and/orwasted energy.

U.S. Pat. No. 5,540,049 (“the '049 patent”) issued to Lunzman disclosesa control system and method for a hydraulic actuator. The '049 patentincludes a hydraulic system having a variable flow hydraulic pumpdelivering fluid under pressure to the hydraulic actuator. The '049patent also includes a closed center valve that operates to control aflow of the hydraulic fluid to the hydraulic actuator and a separatebypass valve that operates to control a flow of the hydraulic fluid to afluid reservoir. A control system, having a separate bypass controllerthat calculates the effect of a closed center valve stroke signal,responsively controls the separate bypass valve. The separate bypasscontroller calculates the effect of the closed center valve strokesignal and derives a signal based on pressure modulation to control theseparate bypass valve.

Although the '049 patent may include a separate bypass valve to controlthe flow of pressurized fluid to a reservoir, it may bypass flow that isrequired by the actuator which may undesirably lower the movement speedof the hydraulic actuator. Additionally, the '049 may require a complexpump and valve control system.

The present disclosure is directed to overcoming one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

In a first aspect, the present disclosure is directed to a hydraulicsystem. The hydraulic system includes a first source of pressurizedfluid and at least one fluid actuator. The hydraulic system furtherincludes a first valve disposed between the first source and the atleast one fluid actuator. The first valve is configured to selectivelycommunicate pressurized fluid from the first source to a tank inresponse to a first command. The first command is at least partiallybased on a predetermined flow area of the first valve.

In another aspect, the present disclosure is directed to a method ofoperating a hydraulic system. The method includes pressurizing a fluidand directing the pressurized fluid toward a first valve. The firstvalve has a first flow passageway and a first valve stem. The methodalso includes selectively directing an amount of the pressurized fluidthrough the flow passageway to a tank. The method further includesselectively varying the area of the flow passageway at least partiallyin response to an operator input and a predetermined flow area of thefirst valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view diagrammatic illustration of an exemplarydisclosed work machine;

FIG. 2 is a schematic illustration of an exemplary hydraulic system ofthe work machine of FIG. 1; and

FIG. 3 is a schematic illustration of an exemplary control algorithm forthe bypass valves of the hydraulic system of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary work machine 10. Work machine 10 may bea fixed or mobile machine that performs some type of operationassociated with an industry such as, for example, mining, construction,farming, or any other industry known in the art. For example, workmachine 10 may be an earth moving machine such as an excavator, abackhoe, a loader, a dozer, a motor grader, or any other earth movingmachine. Work machine 10 may include a frame 12, a work implement 14,hydraulic actuators 18, 20, 22, an operator interface 16, a tractiondevice 24, and a power source 26.

Frame 12 may include any structural unit that supports work machine 10.Frame 12 may be, for example, a stationary base frame connecting powersource 26 to traction device 24, a movable frame member of a linkagesystem connecting work implement 14 to traction device 24 and powersource 26, or any other type of frame known in the art.

Work implement 14 may include any device used in the performance of atask and may be controllable by operator interface 16. For example, workimplement 14 may include a blade, a bucket, a shovel, a ripper, apropelling device, and/or any other task-performing device known in theart. Work implement 14 may be connected to frame 12 via a direct pivot,via a linkage system with hydraulic actuators 18, 20, 22 forming one ormore members in the linkage system, or in any other appropriate manner.Work implement 14 may be configured to pivot, rotate, slide, swing,and/or move relative to frame 12 in any other manner known in the art.

Operator interface 16 may be configured to receive input from anoperator indicative of a desired operation, such as, for example,movement of work implement 14, movement of traction device 24, movementof frame 12, and/or any other suitable operation of work machine 10.Specifically, operator interface 16 may include one or more operatorinterface devices 28 that may include proportional-type controllersconfigured to position and/or orient components of work machine 10, suchas, for example, a multi-axis joystick located to one side of anoperator station. It is contemplated that additional and/or differentoperator interface devices 28 may be included within operator interface16 such as, for example, wheels, knobs, push-pull devices, switches,pedals, and other operator interface devices known in the art.

Hydraulic actuators 18, 20, 22 may each include a piston-cylinderarrangement, a hydraulic motor, and/or any other known hydraulicactuator having one or more fluid chambers therein. For example,hydraulic actuators 18, 20, 22 may each include a tube defining acylinder and a piston separating the cylinder into a first chamber and asecond chamber. Pressurized fluid may be selectively supplied to thefirst and second chambers to create a pressure differential across thepiston affecting movement of the piston relative to the tube. Theresulting expansion and retraction of each of hydraulic actuators 18,20, 22 may function to assist in moving frame 12 and/or work implement14.

Traction device 24 may include tracks located on each side of workmachine 10 (only one side shown). Alternately, traction device 24 mayinclude wheels, belts, or other traction devices. Traction device 24 mayor may not be steerable. It contemplated that traction device 24 may behydraulically controlled, mechanically controlled, electronicallycontrolled, or controlled in any other suitable manner.

Power source 26 may include an engine such as, for example, a dieselengine, a gasoline engine, a gaseous fuel driven engine, or any otherengine known in the art. Power source 26 may be configured to supplyenergy to the various components of work machine 10, such as, forexample, traction device 24. It is contemplated that power source 26 mayalternately include another source of power such as a fuel cell, a powerstorage device, an electric or hydraulic motor, and/or another source ofpower known in the art.

As illustrated in FIG. 2, work machine 10 may further include a controlsystem 100 and a hydraulic system 200 to affect the operation of workmachine 10. Control system 100 may include various components thatcooperate to affect the operation of hydraulic system 200. Specifically,control system 100 may be configured to receive operator inputs viaoperator interface devices 28 and operate one or more components ofhydraulic system 200 in response thereto. Hydraulic system 200 mayinclude various components that cooperate to affect the operation of oneor more components of work machine 10. Specifically, hydraulic system200 may be configured to manipulate the pressure and/or flow of apressurized fluid to affect movement of hydraulic actuators 18, 20, 22and, as a result, affect movement of, for example, work implement 14and/or frame 12.

Control system 100 may include a controller 104 and communication lines106, 108, 110, 112, and 114. Controller 104 may include a singlemicroprocessor or multiple microprocessors configured to control theoperation of hydraulic system 200. Controller 104 may include a memory,a data storage device, a communications hub, and/or other componentsknown in the art. It is contemplated that controller 104 may beconfigured as a separate controller and/or be integrated within ageneral work machine control system capable of controlling variousadditional functions of work machine 10.

Controller 104 may be configured to receive inputs from operatorinterface device 28 via communication line 106. Controller 104 may alsobe configured to access one or more relational databases, such as, forexample, maps, equations, and/or look-up tables. Controller 104 maycommand a first and second source 202, 204 of pressurized fluid and afirst and second bypass valve 208, 210 based on the received inputs andthe accessed databases. For example, controller 104 may issue areacommands, via communication lines 112, 114 to first and second bypassvalves 208, 210, respectively. Controller 104 may also issue flowcommands, via communication lines 108, 110 to operate first and secondsources 202, 204, respectively.

Hydraulic system 200 may include, in addition to first and secondsources 202, 204 and first and second bypass valves 208, 210, a tank206, hydraulic components 212, 214, 216, 218, combiner valve 230, arelief valve 232, and check valves 262, 264, 266, 268. Hydraulic system200 may further include several passageways 250, 252, 254, 256, 258, 260fluidly connecting the various components thereof. Hydraulic system 200may be configured to selectively direct the flow of pressurized fluidfrom first and second sources 202, 204 to selectively affect movement ofhydraulic actuators 18, 20, 22. It is contemplated that hydraulic system200 may include additional and/or different components such as, forexample, pressure sensors, temperature sensors, position sensors,restrictive orifices, accumulators, and/or other components known in theart.

First and second sources 202, 204 may be configured to produce a flow ofpressurized fluid and may include a variable displacement pump such as,for example, a swash plate pump, a variable pitch propeller pump, and/orother sources of pressurized fluid known in the art. First and secondsources 202, 204 may be drivably connected to power source 26 by, forexample, a countershaft, a belt, an electrical circuit, or in any othersuitable manner. First and second sources 202, 204 may be disposedbetween tank 206 and hydraulic components 212, 214, 216, 218.

Tank 206 may include a reservoir configured to hold a supply of fluid.The fluid may include, for example, a dedicated hydraulic oil, an enginelubrication oil, a transmission lubrication oil, or any other workingfluid known in the art. One or more hydraulic systems within workmachine 10 may draw fluid from and return fluid to tank 206. It is alsocontemplated that hydraulic system 200 may be connected to multipleseparate fluid tanks.

First and second bypass valves 208, 210 may each be configured toregulate a flow of pressurized fluid to tank 206. First bypass valve 208may be disposed between first source 202 and first upstream passageway250. Second bypass valve 210 may be disposed between second source 204and second upstream passageway 252. Specifically, first and secondbypass valves 208, 210 may each include a spring biased valve stemsupported in a valve bore. The valve stem may be solenoid actuated andconfigured to proportionally move between a first position at whichfluid flow is blocked from flowing to tank 206 and a second position atwhich a maximum fluid flow is allowed to flow to tank 206. Proportionalmovement of the valve stem between the first position and the secondposition may allow an increasing flow of pressurized fluid to flow totank 206. It is contemplated that the proportional valve stem may varythe flow of pressurized fluid in any manner known in the art, such as,for example, linearly. It is also contemplated that first and secondbypass valves 208, 210 may alternately be hydraulically actuated,mechanically actuated, pneumatically actuated, or actuated in any othersuitable manner.

Hydraulic components 212, 214, 216, 218 may each include one or morevalves and/or fluid passageways configured to selectively communicatepressurized fluid from a respective one of first and second upstreampassageways 250, 252 to an associated hydraulic actuator 18, 20, 22 andselectively communicate pressurized fluid from an associated hydraulicactuator 18, 20, 22 to a respective one of first and second downstreampassageways 254, 256. Pressurized fluid communicated to and fromassociated hydraulic actuators 18, 20, 22 may affect movement thereof.It is contemplated that two or more hydraulic components 212, 214, 216,218 may cooperate to jointly affect movement of a single hydraulicactuator. It is also contemplated that controller 104 may control theoperation of hydraulic components 212, 214, 216, 218. For clarificationpurposes, only hydraulic component 212 will be explained below. It isnoted, however, that explanation thereof is applicable to hydrauliccomponents 214, 216, 218.

Hydraulic component 212 may include a single- or multi-valve arrangementconfigured to selectively communicate pressurized fluid from firstupstream passageway 250 to the first and second chambers of hydraulicactuator 18 and to selectively communicate pressurized fluid from thefirst and second chambers of hydraulic actuator 18 to first downstreampassageway 254 to affect movement of hydraulic actuator 18. For example,hydraulic component 212 may include first and second component valves todirect pressurized fluid from upstream passageway 250 to the first andsecond chambers of hydraulic actuator 18, respectively and may includethird and fourth component valves to direct pressurized fluid from thefirst and second chambers of hydraulic actuator 18 to first downstreampassageway 254. It is contemplated that elements of hydraulic component212 may be controlled by controller 104 and/or by a separate controller.It is also contemplated that hydraulic component 212 may further includevarious other components, such as, pressure sensors, accumulators,temperature sensors, and/or other components known in the art.

First upstream passageway 250 and second upstream passageway 252 may befluidly connected by combiner valve 230. Combiner valve 230 may includea spring biased valve stem supported in a valve bore. The valve stem maybe solenoid actuated and configured to move between a first position anda second position. Combiner valve 230 may, in the first position, allowfluid to flow from first upstream passageway 250 to second upstreampassageway 252 and block fluid flow from second upstream passageway 252to first upstream passageway 250, by, for example, an appropriatelyorientated check valve. Combiner valve 230 may, in the second position,allow pressurized fluid to freely flow to and from both first and secondupstream passageways 250, 252. It is contemplated that combiner valve230 may be controlled by controller 104, and may be hydraulicallyactuated, mechanically actuated, pneumatically actuated, or actuated inany other suitable manner. It is also contemplated that combiner valve230 may alternatively include a two position valve configured to movebetween a fist position allowing fluid to flow between first upstreampassageway 250 and second upstream passageway 252 and a second positionblocking fluid flow between first upstream passageway 250 and secondupstream passageway 252. It is further contemplated that combiner valve230 may include any number of positions each configured to allow,substantially block in both directions, and/or substantially block in asingle direction fluid flow between first and second upstreampassageways 250, 252

Relief valve 232 may be fluidly connected downstream of first and secondsources 202, 204. Relief valve 232 may have a valve element springbiased toward a valve closing position and movable to a valve openingposition in response to a pressure downstream of first and secondsources 202, 204 being above a predetermined pressure. In this manner,relief valve 232 may be configured to reduce a pressure spike withinhydraulic system 200 by allowing pressurized fluid to drain to tank 206.

Hydraulic system 200 may further include several check valves 262, 264,266, 268 to control the flow of the pressurized fluid. Specifically,hydraulic system 200 may include a first check valve 262 to allow flowfrom first fluid passageway 258 to relief valve 232 and to block flowfrom relief valve 232 to first fluid passageway 258. Similarly,hydraulic system 200 may include a second check valve 264 to allow flowfrom second fluid passageway 260 to relief valve 232 and to block flowfrom relief valve 232 to second fluid passageway 260. Accordingly, firstand second check valves 262, 264 may prohibit flow of pressurized fluidfrom tank 206 to first and second fluid passageways 258, 260. Hydraulicsystem 200 may also include a third check valve 266 to allow flow ofpressurized fluid from first fluid passageway 258 to first upstreamfluid passageway 250 and block flow of pressurized fluid from firstupstream fluid passageway 250 to first fluid passageway 258. Similarly,hydraulic system 200 may include a fourth check valve 268 to allow flowof pressurized fluid from second fluid passageway 260 to second upstreamfluid passageway 252 and to block flow of pressurized fluid from secondupstream fluid passageway 252 to second fluid passageway 260.Accordingly, third and fourth check valves 266, 268 may prohibit flow ofpressurized fluid from first source 202 to second bypass valve 210 andprohibit flow of pressurized fluid from second source 204 to firstbypass valve 208.

FIG. 3 illustrates an exemplary algorithm 300 for controlling first andsecond bypass valves 208, 210. For clarification purposes only,algorithm 300 will be explained below with reference to first source 202and first bypass valve 208. It is noted, however, that algorithm 300 isapplicable to second source 204 and second bypass valve 210.

Algorithm 300 may be configured to receive input signals from operatorinterface device 28 and output signals to control first bypass valve 208and first source 202. Algorithm 300 may be configured to receive anoperator interface command 302, access relational database 304 todetermine a bypass area and, establish a bypass command 312. Algorithm300 may also access relational databases 306, 308 to determine anestimated bypass flow and a source flow, respectively, and add theestimated bypass flow and the source flow (step 310) to establish asource command 314. It is noted that the diagrammatic representations ofrelational databases 304, 306, and 308 in FIG. 3 are for illustrativepurposes only and actual any relationships represented thereby may be inthe form of any function, curve, table, map and/or other relationshipknown in the art.

Operator interface command 302 may include a signal configured to beindicative of a position of operator interface device 28. Operatorinterface command 302 may embody any signal, such as, for example, apulse, a voltage level, a magnetic field, a sound or light wave, and/orother signal format known in the art. It is contemplated that operatorinterface command 302 may be directly or indirectly indicative of aposition of a position operator interface device 28, such as, forexample, being indicative of a lever position, being indicative of apressure of fluid operating pilot valves in a secondary hydrauliccircuit and/or being indicative of any other secondary command orindicator representative of a position of an operator interface device.It is also contemplated that operator interface command 302 may includea combination of component commands and/or indicators.

Relational database 304 may be configured to functionally relateoperator interface positions to predetermined bypass areas. Relationaldatabase 304 may include one or more relational maps that may be in theform of, for example, a two- or three-dimensional look-up table and/oran equation and may relate any number of inputs to establish a bypassarea. Specifically, relational database 304 may include a look-up tablerelating operator interface positions to predetermined bypass areas toprovide a desired amount of flow area through which pressurized fluidmay flow. The desired amount of flow area may correspond to the amountof feedback provided to an operator. For example, a particular operatorinterface command 302 may establish a particular bypass command 312 toestablish a desired flow area of first bypass valve 208 to provide adesired feedback to an operator. It is contemplated that interpolationand/or an equation may be used to relate received operator interfacesignals and operator interface signals within the look-up table. It isalso contemplated that relational database 304 may be populated withdata determined from test equipment, data from predeterminedrelationships, data selected or desired by one or more operators, and/ordata determined by any other suitable manner.

Relational database 306 may be configured to functionally relateoperator interface positions to estimated bypass flows. Relationaldatabase 306 may include one or more relational maps that may be in theform of, for example, a two- or three-dimensional look-up table and/oran equation and may relate any number of inputs to establish anestimated bypass flow. Specifically, relational database 306 may includea look-up table relating operator interface positions to predeterminedestimated bypass flows. For example, a particular operator interfacecommand 302 may establish an estimated bypass flow based in part on thedetermined bypass area and the estimated flow of pressurized fluidtherethrough. It is contemplated that relational database 306 mayalternatively include a look-up table relating bypass areas to estimatedbypass flows. It is also contemplated that interpolation and/or anequation may be used to relate received operator interface signals andestimated bypass flows within the look-up table. It is furthercontemplated that relational database 304 may be populated with datadetermined from test equipment, data from predetermined relationships,data selected or desired by one or more operators, and/or datadetermined by any other suitable manner.

Relational database 308 may be configured to functionally relateoperator interface positions and source flows. Relational database 308may include one or more relational maps that may be in the form of, forexample, a two- or three-dimensional look-up table and/or an equationand may relate any number of inputs to establish a source flow.Specifically relational database 308 may include a look-up tablerelating operator interface positions to predetermined source flows. Forexample, a particular operator interface command 302 may establish asource flow based in part on the desired flow or amount of pressurizedfluid required to operate one or more of hydraulic actuators 18, 20, 22.It is contemplated that interpolation and/or an equation may be used torelate received operator interface signals and estimated bypass flowswithin the look-up table. It is also contemplated that relationaldatabase 304 may be populated with data determined from test equipment,data from predetermined relationships, data selected or desired by oneor more operators, and/or data determined by any other suitable manner.

Control algorithm 300 may add the determined estimated bypass flow andthe determined source flow for a given operator interface command 302.The determined estimated bypass flow and the determined source flow maybe added by combining the respective flows into a single flow command.For example, the determined estimated bypass flow and the determinedsource flow may be summed together to establish a single source command314. Adding the estimated bypass flow and the source flow may provide anappropriate amount of pressurized fluid to hydraulic system 200 tosatisfy both an actuator requirement and a bypass valve requirement.

Bypass command 312 may include a signal configured to energize thesolenoid associated with bypass valve 208 to move the valve stem ofbypass valve 208 relative to the valve bore of bypass valve 208 to varythe flow area thereof. Bypass command 312 may embody any signal, suchas, for example, a pulse, a voltage level, a magnetic field, a sound orlight wave, and/or other signal format known in the art. Source command314 may include a signal configured to actuate source 202 to movecomponents thereof to vary the flow rate and/or pressure of source 202.Source command 314 may embody any signal, such as, for example, a pulse,a voltage level, a magnetic field, a sound or light wave, and/or othersignal format known in the art.

INDUSTRIAL APPLICABILITY

The disclosed hydraulic system may be applicable to any work machinethat includes a hydraulic actuator. The disclosed hydraulic system mayreduce energy necessary to operate the hydraulic actuator, may provideappropriate operator feedback, may be applicable to multi-sourcesystems, and/or may provide a simple bypass control configuration. Theoperation of hydraulic system 200 is explained below.

Referencing FIG. 2, first and second sources 202, 204 may receive fluidfrom tank 206 and supply pressurized fluid to first and second fluidpassageways 258, 260 and first and second upstream fluid passageways250, 252, respectively. As such, pressurized fluid may be supplied toupstream sides of first and second bypass valves 208, 210 and toupstream sides of each of first, second, third, and fourth hydrauliccomponents 212, 214, 216, 218. Additionally, pressurized fluid may besupplied to both sides of combiner valve 230. Initially, first andsecond sources 202, 204 may supply pressurized fluid to hydraulic system200 at a minimum pressure and flow rate. The minimum pressure and flowrate may be determined by, for example, a minimum swashplate angle of aswashplate pump. First and second bypass valves 208, 210 may each beactuated to an initial flow area at which substantially all of theminimum flow rate supplied by first and second sources 202, 204 may bedirected to tank 206.

One or more of hydraulic actuators 18, 20, 22 may be movable by fluidpressure in response to operator inputs. An operator may actuateoperator interface device 28 to a desired position to affect control ofa component of work machine 10, such as, for example, work implement 14.Operator interface device 28 may transmit an operator interface command302 (FIG. 3) to controller 104, via communication line 106, indicativeof the relative position of operator interface device 28. Controller 104may receive operator interface command 302 for use within algorithm 300.

Referencing FIG. 3, controller 104 may be configured to executealgorithm 300 in response to operator interface command 302.Specifically, algorithm 300 may be configured to determine a bypassarea, an estimated bypass flow, and a source flow at least partiallybased on operator interface command 302. Algorithm 300 may determine anappropriate bypass area via relational database 304, determine anappropriate estimated bypass flow via relational database 306, anddetermine an appropriate source flow via operational database 308.

Algorithm 300 may further be configured to generate bypass command 312and source command 314 at least partially based on the determined bypassarea, estimated bypass flow, and source flow. Specifically, algorithm300 may generate bypass command 312 in proportion to a desired bypassflow area. Algorithm 300 may generate source command 314 in proportionto the sum of the estimated bypass flow and the determined source flow.Algorithm 300 may sum the estimated bypass flow and the source flow toprovide an appropriate amount of flow to hydraulic system 200 to performthe operation desired by an operator. For example, if the estimatedbypass flow was not added to the determined source flow, one or morehydraulic actuators 18, 20, 22 may not receive the demanded flow ofpressurized fluid because a portion of the source flow may be divertedto tank 206 via one or both of first and second bypass valves 208, 210(FIG. 2).

Controller 104 may be configured to communicate bypass command 312 toone of first and second bypass valves 208, 210 via communication lines112, 114 (FIG. 2) and may be configured to communicate source command314 to one of first and second sources 202, 204 via communication lines108, 110 (FIG. 2). It is contemplated that algorithm 300 may be repeatedto generate a bypass command for each one of first and second bypassvalves 208, 210 and to generate a source command for each one of firstand second sources 202, 204. It is further contemplated that algorithm300 may, alternatively, be configured to simultaneously determine firstand second bypass commands to control first and second bypass valves208, 210, respectively, and to determine first and second sourcecommands to control first and second sources 202, 204, respectively.

Again referencing FIG. 2, in response to a bypass command communicatedfrom controller 104 to first bypass valve 208 via communication line112, the valve stem of first bypass valve 208 may be actuated to a firstopen position. Similarly, in response to a bypass command communicatedfrom controller 104 to second bypass valve 210 via communication line114, the valve stem of second bypass valve 210 may be actuated to asecond open position. Additionally, first and second sources 202, 204may be operated to deliver respective flows of pressurized fluid tofirst and second fluid passageways 258, 260 in response to first andsecond source commands communicated from controller 104 viacommunication lines 108, 110. Furthermore, controller 104 may controlthe operation of one or more of hydraulic components 212, 214, 216, 218to selectively operate one or more of hydraulic actuators 18, 20, 22.

For example, an operator may desire extension or retraction of hydraulicactuator 18. For explanation purposes only, hydraulic component 212 maycontrol the movement of hydraulic actuator 18. As such, operator inputsvia operator interface device 28 may, via controller 104, selectivelycommand first and second sources 202, 204 to establish first and secondflows of pressurized fluid, selectively command first and second bypassvalves 208, 210 to direct first and second bypass flows of pressurizedfluid to tank 206, and may selectively actuate one or more valves ofhydraulic component 212 to direct flows of pressurized fluid to and fromhydraulic actuator 18.

The first flow of pressurized fluid from first source 202 may bedirected to hydraulic component 212 via first fluid passageway 258 andfirst upstream passageway 250. A portion of the first flow ofpressurized fluid may be directed to tank 206 through first bypass valve208. The amount of the first flow of pressurized fluid directed to tank206 may be directly proportional to the amount first bypass valve 208 isopen, e.g., the larger the flow area of first bypass valve 208 thegreater the amount of the first flow of pressurized fluid diverted totank 206. It is contemplated that a larger flow area of first bypassvalve 208 may correspond to a greater feedback provided to an operatorby, for example, bypassing more flow of pressurized fluid to tank 206during a resistive movement of hydraulic actuator 18. It is alsocontemplated that hydraulic actuator 18 may only require pressurizedfluid from first source 202. As such, the second flow may besubstantially equal to the minimum flow of pressurized fluid from secondsource 204 and second bypass valve 210 may remain at the initialposition to continue to divert substantially all of the minimum flow ofpressurized fluid from second source 204 to tank 206.

For another example, an operator may desire an extension or retractionof hydraulic actuator 20. For explanation purposes only, hydrauliccomponents 214, 216 may control the movement of hydraulic actuator 20.As such, operator inputs via operator interface device 28 may, viacontroller 104, selectively command first and second sources 202, 204 toestablish first and second flows of pressurized fluid, selectivelycommand first and second bypass valves 208, 210 to direct first andsecond bypass flows of pressurized fluid to tank 206, and mayselectively actuate one or more valves of hydraulic components 214, 216to direct flows of pressurized fluid to and from hydraulic actuator 20.It is contemplated that hydraulic actuator 20 may require flow ofpressurized fluid from both first and second sources 202, 204 foractuation thereof. It is also contemplated that hydraulic actuator 20may include two hydraulic actuators operating together and hydrauliccomponent 214 may direct pressurized fluid to one of the two hydraulicactuators and hydraulic component 216 may direct pressurized fluid tothe other of the two hydraulic actuators.

The first flow of pressurized fluid from first source 202 may bedirected to hydraulic component 214 via first fluid passageway 258 andfirst upstream passageway 250. A portion of the first flow ofpressurized fluid may be directed to tank 206 through first bypass valve208. The amount of the first flow of pressurized fluid directed to tank206 may be proportional to the amount first bypass valve 208 is open,e.g., the larger the flow area of first bypass valve 208 the greater theamount of the first flow of pressurized fluid diverted to tank 206.Because hydraulic actuator 20 may require two hydraulic components foractuation thereof, a second flow of pressurized fluid from second source204 may be directed to hydraulic component 216 via second fluidpassageway 260 and second upstream passageway 252. A portion of thesecond flow of pressurized fluid may be directed to tank 206 throughsecond bypass valve 210. Similar to first bypass valve 208, the amountof the second flow of pressurized fluid directed to tank 206 may beproportion to the amount of second bypass valve 210 is open. As notedabove, a larger flow area of first and/or second bypass valves 208, 210may correspond to a greater feedback provided to an operator by, forexample, bypassing a greater flow of pressurized fluid to tank 206during a resistive movement of hydraulic actuator 20.

For yet another example, an operator may desire extension or retractionof hydraulic actuator 22. For explanation purposes only, hydrauliccomponent 218 may control the movement of hydraulic actuator 22. Assuch, operator inputs via operator interface device 28 may, viacontroller 104, selectively command first and second sources 202, 204 toestablish first and second flows of pressurized fluid, selectivelycommand first and second bypass valves 208, 210 to direct first andsecond bypass flows of pressurized fluid to tank 206, and mayselectively actuate one or more valves of hydraulic component 212 todirect flows of pressurized fluid to and from hydraulic actuator 22.

The second flow of pressurized fluid from second source 204 may bedirected to hydraulic component 218 via second fluid passageway 260 andsecond upstream passageway 252. A portion of the second flow ofpressurized fluid may be directed to tank 206 through second bypassvalve 210. The amount of the second flow of pressurized fluid directedto tank 206 may be directly proportional to the amount second bypassvalve 210 is open, e.g., the larger the flow area of second bypass valve210 the greater the amount of the first flow of pressurized fluiddiverted to tank 206. It is contemplated that a larger flow area ofsecond bypass valve 210 may correspond to a greater feedback provided toan operator by, for example, bypassing more flow of pressurized fluid totank 206 during a resistive movement of hydraulic actuator 22. It isalso contemplated that hydraulic actuator 22 may only requirepressurized fluid from second source 204. As such, the first flow may besubstantially equal to the minimum flow of pressurized fluid from firstsource 202 and first bypass valve 208 may remain at the initial positionto continue to divert substantially all of the minimum flow ofpressurized fluid from first source 204 to tank 206.

In multi-function operation where, for example, more than one ofhydraulic actuators 18, 20, 22 may be simultaneously actuated, multiplebypass commands may be established for each of first and second bypassvalves 208, 210. It is contemplated that controller 104 may communicatethe bypass command that would control a respective bypass valve to thegreatest flow area. For example, if it was desired to operate bothhydraulic component 212 and 218 simultaneously, component 212 mayestablish first bypass valve 208 to a non-minimum flow area andcomponent 218 may establish first bypass valve 208 to the minimum flowarea. As such, controller 104 may control first bypass valve 208 to thenon-minimum flow area. Similarly, control of component 218 may establishsecond bypass valve 210 to a non-minimum flow area and component 212 mayestablish second bypass valve 210 to the minimum flow area. As such,second bypass valve 210 may be controlled to the non-minimum flow area.It is contemplated that controlling first and second bypass valves 208,210 to the greatest flow area in multi-function operations may providean appropriate feedback to an operator by, for example, ensuring thatmore feedback is provided to an operator rather than less feedback. Itis also contemplated that in single- and/or multi-function operation,first and second bypass valves may be controlled to any flow areabetween a fully closed position and a fully opened position, as desired.

Combiner valve 230 may be actuated between the first position allowingfluid flow between first and second upstream fluid passageways 250, 252and the second position blocking fluid flow from second upstreampassageway 252 to first upstream passageway 250 in response to theoperation of one or more of hydraulic components 212, 214, 216, 218. Forexample, during operation of hydraulic components 214, 216, combinervalve 230 may be in the first position to thereby allow first and secondflows of pressurized fluid from first and second sources 202, 204 tocombine within first and second upstream passageways 250, 252 allowingfirst and second sources 202, 204 to cumulatively supply a combined flowof pressurized fluid to hydraulic components 214, 216. For anotherexample, during operation of hydraulic component 218, combiner valve 230may be in the second position to thereby block the second flow ofpressurized fluid from second source 204 from being diverted away fromhydraulic component 218 and into first upstream passageway 250.

Because hydraulic system 200 includes first and second bypass valves208, 210, it may provide improved operator feedback during operation ofwork machine 10. As discussed above, when movement of an actuator 18,20, 22 is resisted by an external load, pressure within hydraulic system200 may increase resulting in an increased flow of pressurized fluidthrough first and/or second bypass valve 208, 210. This increased flowmay be sensed by an operator by, for example, a decrease in actuationspeed, to indicate the encountered resistance. Additionally, becausebypass flow and source flow may be combined, hydraulic system 200 mayprovide sufficient flow of pressurized fluid to a plurality of hydraulicactuators while maintaining sufficient operator feedback. Furthermore,because first and second bypass valves 208, 210 may divert the minimumflows from first and second sources 202, 204, pressure build-up withinhydraulic system 200 may be reduced. Finally, controlling bypass valves208, 210 by area commands may provide simple control of hydraulic system200 and allow for flexible and accurate control of pressurized fluid toand from hydraulic actuators 18, 20, 22.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed hydraulicsystem having area controlled bypass. Other embodiments will be apparentto those skilled in the art from consideration of the specification andpractice of the disclosed hydraulic system. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

1. A hydraulic system comprising: a first source of pressurized fluid;at least one fluid actuator; a first valve disposed between the firstsource and the at least one fluid actuator being configured toselectively communicate pressurized fluid from the first source to atank in response to a first command; and a controller configured todetermine the first command by determining a plurality of commands forthe first valve and selecting one of the plurality of commands as thefirst command.
 2. The hydraulic system of claim 1 wherein the at leastone fluid actuator is a first plurality of fluid actuators, thehydraulic system further including a first passageway fluidlycommunicating the first source, the first valve, and the first pluralityof fluid actuators.
 3. The hydraulic system of claim 1, wherein thecontroller is further configured to receive an operator input andcommunicate the first command to the first valve and communicate asecond command to the first source.
 4. The hydraulic system of claim 3,wherein the second command is at least partially based on an estimatedamount of flow of pressurized fluid through the first valve and apredetermined amount of pressurized fluid flow through the first source.5. The hydraulic system of claim 3, wherein: the first command isdetermined via a look-up table relating operator inputs and displacementvalues of the first valve; and the second command is determined by:estimating a first valve flow via a look-up table relating thedisplacement values of the first valve and first valve flows,determining a first source flow via a look-up table relating operatorinputs and first source flows, and adding the estimated first valve flowand the determined first source flow.
 6. The hydraulic system of claim1, further including: a second source of pressurized fluid; a secondplurality of fluid actuators; and a second valve disposed between thesecond source and the second plurality of fluid actuators, the secondvalve being movable in response to a third command, the third commandbeing at least partially based on a predetermined flow area of thesecond valve.
 7. The hydraulic system of claim 6, wherein the at leastone actuator is a first plurality of actuators, the hydraulic systemfurther including: a first passageway fluidly communicating the firstsource, the first valve, and the first plurality of fluid actuators; anda second passageway fluidly communicating the second source, the secondvalve, and the second plurality of fluid actuators.
 8. The hydraulicsystem of claim 7, further including: a third valve disposed downstreamof the first and second valves and being configured to selectivelyfluidly communicate pressurized fluid from the second source to at leastone of the first plurality of actuators.
 9. A method of operating ahydraulic system comprising: pressurizing a fluid; directing pressurizedfluid toward a first valve, the first valve having a first flowpassageway and a first valve stem; selectively directing an amount ofthe pressurized fluid through the first flow passageway to a tank; andestimating the flow of pressurized fluid directed through the first flowpassageway.
 10. The method of claim 9, further including selectivelymoving the first valve stem to vary the area of the first flowpassageway.
 11. The method of claim 9, further including: selectivelydirecting pressurized fluid to a first fluid actuator and moving thefirst valve stem to a first position; and selectively communicatingpressurized fluid to a second fluid actuator and moving the first valvestem to a second position; wherein an area of the first flow passagewayin the first position is different than an area of the first flowpassageway in the second position.
 12. The method of claim 9, whereinpressurizing a fluid includes pressurizing a first fluid to a firstpressure and directing the first fluid at a first flow rate, andpressurizing a second fluid to a second pressure and directing thesecond fluid at a second flow rate, the method further including:directing the fluid having the first flow rate toward the first valve;directing the fluid having the second flow rate toward a second valve;selectively permitting at least a portion of the first fluid to flow tothe tank through the first valve; and selectively permitting at least aportion of the second fluid to flow to the tank through the secondvalve.
 13. The method of claim 9, wherein pressurizing a fluid includespressurizing a fluid with a first source, the method further including:determining a first command at least partially based on a look-up tablerelating operator inputs and displacement values of the first valve atleast partially based on the predetermined flow areas; determining asecond command at least partially based on a look-up table relating thedisplacement values of the first valve and estimated valve flow rates;determining a third command at least partially based on a look-up tablerelating operator inputs and first source flow rates; determining afourth command at least partially based on the sum of the second andthird commands; selectively communicating the first command to the firstvalve; and selectively communicating the fourth command to a firstsource of pressurized fluid.
 14. The method of claim 9, furtherincluding: selectively directing pressurized fluid to a first chamber ofa first fluid actuator; selectively directing pressurized fluid from asecond chamber of the first actuator to the tank.
 15. The method ofclaim 14, further including: directing pressurized fluid via a firstfluid passageway toward the first valve and toward the actuator; anddirecting a portion of pressurized fluid from the first fluid passagewayto the tank via the first valve.
 16. A machine comprising: an implement;a frame; a first hydraulic actuator configured to affect movement of theimplement; a second hydraulic actuator configured to affect movement ofat least a part of the frame; a hydraulic system including: a tank,first and second sources of pressurized fluid, a first valve configuredto selectively permit a pressurized fluid flow to the tank in responseto a first area command, and a second valve configured to selectivelypermit a pressurized fluid flow to the tank in response to a second areacommand; and a controller configured to determine first and secondsource commands at least partially based on an estimated flow ofpressurized fluid directed through the first and second valves,respectively.
 17. The machine of claim 16, wherein the controller isfurther configured to selectively communicate the first and second areacommands to the first and second valves, respectively.
 18. The machineof claim 17, wherein the controller is configured to determine the firstand second area commands by determining first and second valvedisplacements at least partially based on first and second look-uptables, each relating operator inputs with predetermined first andsecond valve displacements to determine first and second valve flowareas.
 19. The machine of claim 17 wherein the controller is furtherconfigured to determine the first and second source commands by:estimating first and second fluid flows through the first and secondvalves at least partially based on third and fourth look-up tables, eachrelating valve displacements and fluid flows; determining first andsecond source flows at least partially based on fifth and sixth look-uptables, each relating operator inputs and source flows; adding theestimated fluid flow through the first valve to the determined fluidflow through the first source; and adding the estimated fluid flowthrough the second valve to the determined fluid flow through the secondsource.
 20. The machine of claim 17, wherein: the first valve includes aflow area configured to permit pressurized fluid through the first valveto the tank; and the controller is further configured to: determine aplurality of first area commands based in part on a plurality ofoperator inputs, and communicate the one of the plurality of first areacommands resulting in the largest flow area of the flow passageway tothe first valve.
 21. The machine of claim 17, further including anoperator interface configured to selectively communicate operator inputsto the controller; wherein the controller selectively affects movementof the first and second hydraulic actuators via the hydraulic circuit.